Single layer centrifugation of stallion spermatozoa improves sperm quality compared with sperm washing

This study compared the effect on semen quality of different handling methods used in the preparation of stallion semen doses for artificial insemination. The three methods were (i) extending the ejaculate to 30–50 × 106/ml, (ii) single layer centrifugation (SLC) and (iii) sperm washing (centrifugation without a colloid). An additional treatment was to add seminal plasma (SP) in various proportions to some SLC preparations. The resulting samples were evaluated for sperm motility by computer assisted sperm analysis, membrane integrity using the Nucleocounter SP-100 and chromatin integrity by the sperm chromatin structure assay. SLC samples consistently had better sperm quality than the extended samples. Sperm washing did not confer any beneficial effect compared with the extended samples and these samples had significantly worse sperm quality than the SLC samples (motility, P < 0.01; viability, P < 0.001). There was no evidence to suggest that adding SP to the SLC samples could enhance sperm motility for more than a few hours. Longer term cold storage of spermatozoa in the presence of small concentrations of SP resulted in a reduction in total motility and progressive motility compared with SLC alone. High concentrations of SP were detrimental to sperm survival.